Unless the GT has been lip locking with another cichlid, and dislocated its jaw, it looks like an acute Columnaris infection.
Columnaris is gram negative bacteria that flourishes at water temps above 82'F, and loves detritus on the substrate, and in canister filters to live in.
After a tank is drained, it can live in an inert state in the thin layer of dirt coating on the glass.
It is very communicable (although sometimes species specific), and an antibiotic effective against gram- bacteria is most effective.
I tend to euthanize any fish that gets it, tear down the tank, and bleach everything that touched the tank.
In cooler water it can appear as fungus looking tufts (columns under the microscope) hence the name.
Here is a cichlid I had that arrived with it, and would have infected the entire tank, had it not been noticed in quarantine.
as the jaw atrophies it projects more and more
the fish tends to hover, and not eat.
It is commonly called Duck Lips, (AKA flower horn disease) and in MHO, I believe the strain we are seeing now, originated in FH farms where antibiotics were overused, which created a very super bug variant.